14.7.5.33 SHOW SLAVE HOSTS Syntax

SHOW SLAVE HOSTS

Displays a list of replication slaves currently registered with
the master.

SHOW SLAVE HOSTS should be executed on a
server that acts as a replication master. The statement displays
information about servers that are or have been connected as
replication slaves, with each row of the result corresponding to
one slave server, as shown here:

Server_id: The unique server ID of the
slave server, as configured in the slave server's
option file, or on the command line with
--server-id=value.

Host: The host name of the slave server
as specified on the slave with the
--report-host option. This
can differ from the machine name as configured in the
operating system.

User: The slave server user name as,
specified on the slave with the
--report-user option.
Statement output includes this column only if the master
server is started with the
--show-slave-auth-info
option.

Password: The slave server password as,
specified on the slave with the
--report-password option.
Statement output includes this column only if the master
server is started with the
--show-slave-auth-info
option.

Port: The port on the master to which the
slave server is listening, as specified on the slave with
the --report-port option.

A zero in this column means that the slave port
(--report-port) was not set.

Master_id: The unique server ID of the
master server that the slave server is replicating from.
This is the server ID of the server on which SHOW
SLAVE HOSTS is executed, so this same value is
listed for each row in the result.

Slave_UUID: The globally unique ID of
this slave, as generated on the slave and found in the
slave's auto.cnf file.

SHOW SLAVE HOSTS syntax doesn't display a list of replication slaves when it's configured a daizy-chain replication - A->B->A. When both servers act as masters i.e there's not server breakdown, both servers replicate to each other. So at one time one of them will act as slave so I don't understand why its options wouldn't be visible in this list.

The slave's --report-X parameters have a lot to do with what appears here. They control the hostname, port, username and password. The username and password appear only if --show-slave-auth-info is set on the master.